IB Course Requirements

G.4.1: ‘Explain the use of biotic indices and indicator species in monitoring environmental change’

Biological monitoring and indicator species

What is an indicator species?• Any biological species that defines a trait or

characteristic of the environment:– May indicate a particular ecosystem– May indicate a disease outbreak– May indicate pollution– May indicate species competition – May indicate climate change

Advantages of Biological Monitoring

1. We can detect intermittent pollution2. A specific change in the Biotic index can

indicate a specific type of pollutant3. Food chains can accumulate pollutants

(biomagnification) – particularly in higher trophic levels

Disadvantages of Biological Monitoring

• Distribution of organisms may be patchy so sampling must be done carefully

• Invertebrate organisms tend to be seasonal• Some indicator species show tolerance to

different pollutants

Biological Monitoring is frequently used to evaluate marine or aquatic pollution

• Oysters and mussels are used as indicator species (‘bio-monitors’) to assess environmental pollution of coastal waters

• Mussel Watch!

Indicator species can be monitored to indicate an increase OR decline in biodiversity

• ‘Sentinel Species’• ‘Keystone species’

Keystone species

• These are species which have a disproportionately significant effect on their environment

• Sometimes they are predators

• Sometimes they are ‘ecological engineers’

• Examples: Grizzly Bear, Sea Otters, Sea Stars

Biological Monitoring is frequently used to identify pollution or presence of toxins on

land

• On land, lichens are often used as indicator species since they are sensitive to sulphur dioxide

• ‘Bushy’ lichens need pristine air• Leafy lichens can survive a small amount of

pollution• ‘Crusty’ lichens can survive in heavily polluted air• Regions devoid of lichens may indicate a high

concentration of sulphur dioxide

IB Course Requirements

G.3.1: Calculate the Simpson diversity index for two local communitiesG.3.2: Analyze the biodiversity of the two local communities using the Simpson index

Simpson’s Diversity Index

Is an estimate of DIVERSITYIt estimates RICHNESS and ‘EVEN-NESS’ of an ecosystem

What is the usefulness of a Diversity Index?

They provide information about ‘rarity’ and ‘common-ness’ of species in a community

Diversity indices allow us to monitor diversity over time in changing ecosystems – for example, to monitor effects of pollution or climate change

Diversity indices allow us to compare communities

Diversity indices convert many species into a single number

Limitations!Simpson’s Diversity Index

is more sensitive for common species

(abundant) and LESS sensitive for RARE

species…

So what is ‘species richness’• Indicates species diversity…but• Estimating ‘richness’ alone would provide only a

limited description of a community: it would not tell us anything about relative abundance of the species identified…

For example…

Why is it important to evaluate ‘species even-ness’?

Even-ness: A measure of the relative abundance of species making up the community

The relevance of ‘species even-ness’

Examples of Simpson’s Reciprocal Index1. Equal diversity of species

Examples of Simpson’s Reciprocal Index2. Low species diversity: Domination of a single particular species…

Example 3 of Simpson’s Reciprocal Index Only one species is present

Example 3 of Simpson’s Reciprocal Index Very few individuals of certain species are present